The Yellow "M" (French: La Marque Jaune ("The Yellow Mark")) by the Belgian artist Edgar P. Jacobs is the sixth comic book in the Blake and Mortimer series. It was first published in Tintin magazine between 6 August 1953 and 3 November 1954 and later appeared in book form in 1956.
For some time now London has been terrorized by an enigmatic villain who informs the press in advance of his crimes. He commits daring robberies and leaves behind an "M" in a yellow circle as a signature. When the Imperial State Crown is stolen from the Tower of London, the Home Office assigns Captain Francis Blake to assist Chief Inspector Glenn Kendall of Scotland Yard. Blake in turn calls in his old friend and housemate, Professor Philip Mortimer, who has been on holiday to Scotland but agrees to return to London to help in the enquiry.